Angle of arrival measurement is a method for determining the direction of propagation of a radio-frequency wave incident on an antenna array. Determination of angle of arrival typically involves measuring a difference of signal arrival at individual elements of the array. The measured differences (e.g., delays) allow calculating the angle of arrival.
Such antenna arrays are typically a group of identical antenna elements arranged such that signals received by each element are of different amplitudes and phases. Such antenna elements may be either directional, producing gain with respect to angle, or omnidirectional. In practice, it is difficult to obtain omnidirectional antennas in an array due to mutual coupling. There are a few different general types of antenna arrays. When the array is arranged in a straight line this is called a linear array. Antennas arranged in parallel lines on one plane has a planar array in two dimensions. Many planes in a group of arrays or antennas results in a three dimensional array.
Typically, all antenna elements in an array must be arranged in a symmetrical pattern. This symmetrical pattern, combined with appropriate electrical delay, results in the desired effect of reinforcement or cancellation of the electric field intensity. The same orientation ensures polarization in the same direction in space. Generally, this has resulted in arrays of considerable size and complexity.
One primary application for angle of arrival measurement is the geolocation of wireless devices. In such arrangements, the angle of arrival information from a single antenna array may be utilized to determine, for example, the angular location of the device relative to cell towers for sector switching purposes. Alternatively, direction information from two antenna arrays, or one array at multiple locations, may be combined to determine (e.g., triangulate) the location of the device.